Large steel towers are typically used to support wires carrying high voltages, such as greater than 100 kV. Other structures include those formed of cement or wood. The voltage is typically 3-phase, and at least three wires are supported. FIG. 1 illustrates the top portion of such a tower 10. The tower 10 is grounded by being imbedded in the ground.
Ceramic insulators 12 support the wires 14. The minimum distance between any wire 14 and the tower 10, or between any two wires, is determined by the IEEE National Electric Safety Code. The code takes into account the peak voltage differential, the environment, the type of insulation used, and other factors to set a minimum distance to prevent arcing under expected conditions.
However, when a large bird lands between a wire and the tower, the bird shortens the effective distance between the wire and the tower, and an arc (also referred to as flashover) may result, creating a short circuit through the bird, which trips a circuit breaker in the distribution system. The bird is, of course, killed.
Various techniques have been used to make the steel tower angled struts 16 and horizontal arms 18 less appealing to a bird, such as by affixing a strip of needles or thin spikes along the struts and arms. Large birds have been known to be injured by the needles and spikes when trying to land on them due to the high speed and momentum of the birds when landing.
It is also known to provide an insulating plastic shield over and along the wire near the insulator 12 that extends a few feet along the wire in both directions. However, the bird may still alight on the grounded tower and create a short circuit with the wire above it. Also, the plastic shields attached to the wires have a large surface area and act to push the wires (and ceramic insulators) closer to the tower under high winds. Further, the wires have to be de-energized in order for the lineman to install the shields over the wires.